Lymph is a clear, yellowish fluid that flows through your body in a network of vessels separate from your blood vessels. While blood carries oxygen and nutrients through arteries and veins, lymph quietly does different but equally important work: it collects waste products from your cells, fights infections, and returns leaked fluid back to your bloodstream.

When you get sick, you might notice swollen lumps in your neck, armpits, or groin. These are lymph nodes, small bean-shaped filters where lymph passes through and immune cells attack germs. The swelling means your lymph system is working hard to fight off an infection.

Your body makes about three liters of lymph every day. Unlike blood, which gets pumped by your heart, lymph moves through muscle contractions and one-way valves, flowing slowly but steadily.

The lymphatic system includes lymph vessels, lymph nodes, the spleen, and the thymus. Together, these organs and tissues form one of your body's main defense systems against disease. Without lymph constantly cleaning up cellular waste and patrolling for invaders, you couldn't stay healthy.